In an image forming apparatus such as a multi function peripheral (MFP) or a printer, there is an apparatus for transferring a toner image formed on a transfer belt to a sheet while the sheet is nipped and conveyed by the transfer belt and a transfer roller.
In the apparatus in which the sheet is nipped and conveyed by the transfer belt and the transfer roller at the time of the transfer, there is a fear that a transfer blur occurs due to the fluctuation of the conveying speed of the transfer belt. There is a fear that the speed of the transfer belt is fluctuated when the leading edge of the sheet enters between the transfer belt and the transfer roller, or the trailing edge of the sheet comes out from between the transfer belt and the transfer roller. There is a fear that the speed of the transfer belt is fluctuated when the sheet is extending between the registration roller and the transfer belt and the trailing edge of the sheet comes out from the registration roller. There is a fear that the speed of the transfer belt is fluctuated when the sheet is nipping by the transfer belt and the transfer roller and the leading edge of the sheet enters the fixing roller.
Hitherto, for example, Japanese Patent Application No. 2006-095763 discloses an apparatus for preventing the conveying speed of a sheet from abruptly increasing when the trailing edge of the sheet comes out from a registration roller.
However, the apparatus of the related art does not prevent the conveying speed of a transfer belt from changing.
Then, the development of a transfer belt unit of an image formation apparatus is desired in which the speed fluctuation of a transfer belt is suppressed irrespective of the operation of a sheet, so that a transfer blur is prevented, and a high quality image can be obtained.